A variety of different applications use sensor systems to detect the movement of an underlying object. For example, inertial sensors, e.g., accelerometers or gyroscopes, are used in safety and navigation systems for automotive, military, aerospace and marine applications. Sensors may be formed using micromachining processes and may include microelectromechanical systems (MEMS). In MEMS devices, certain micromachined structures are designed to move relative to a substrate and other micromachined structures in response to forces applied in a predetermined manner, such as along a predetermined axis of the device. The movement of certain of the structures permits the generation of signals proportional to the magnitude, direction, and/or duration of the force.
For example, one type of MEMS accelerometer employs a movable mass constructed with fingers adjacent and parallel to fingers of one or more fixed, non-moving structures, with all of these structures suspended in a plane above the substrate. The movable structure and the fixed structure form a capacitor, having a capacitance that changes when the movable structure moves relative to the fixed structure in response to the force. Exemplary MEMS accelerometers are discussed in greater detail in U.S. Pat. No. 5,939,633 and exemplary MEMS gyroscopes are discussed in greater detail in U.S. Pat. No. 6,505,511, the disclosures of which are incorporated herein by reference in their entireties.
MEMS devices typically rely on fixed, rigid stoppers to prevent the movable mass from contacting other components or parts during a shock event. For example, if a finger from the movable structure moves into contact with a corresponding fixed finger, the fingers may stick due to electrostatic attraction, causing the device to fail. Moreover, excessive shock to the device may generate large impact forces that may break the MEMS structures or dislocate particles on the mass or fixed structures. These broken or dislocated components undesirably may fall into critical sensing areas and render the sensor inoperative. Furthermore, continuous shock may keep the mass contacting the stopper, thus wearing out the stoppers and causing stiction or electrostatic capture failures.